MARS EXPRESS SPICAM  GEOMETRY FILES Description                               
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Revisions                                                                     
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2008 03 10    V013 correction following new geometry file version (V14)       
2007 07 08    V012 correction following new geometry file version (V13)       
2005 11 18    V011 correction following new geometry file version (V10)       
2004 10 12    V010 initial dimarellis                                         
                                                                              
                                                                              
Purpose                                                                       
                                                                              
     This document describes the contents of the geometry files which         
     are delivered in the Spicam data product.                                
                                                                              
                                                                              
                                                                              
Introduction                                                                  
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     All informations needed to read the geometry file are given.             
                                                                              
                                                                              
     This document is organized as:                                           
         Introduction                                                         
         Overview                                                             
         Header contents                                                      
         Definitions                                                          
         Computation background                                               
                                                                              
Overview:                                                                     
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The geometry file is an ASCII file.                                           
                                                                              
For each UV or IR data file, a geometry file is computed.                     
The geometrical parameters are computed at the time of the UV or IR data      
(which is not the time of the measurement itself, see SPICAM_UVCALIB_DESC.TXT)
                                                                              
This file is computed with SPICE/Naif tools and kernels.                      
                                                                              
The ASCII file is made of 2 parts:                                            
    a header part                                                             
    a list of parameters, one row for each time                               
                                                                              
The header is easily readable and gives all informations on the parameters.   
                                                                              
                                                                              
Header contents:                                                              
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The following informations are listed in the header:                          
    Software version and date used for computation                            
    Filename                                                                  
    List of SPICE kernels                                                     
    SUN information at the first time of the file                             
    Target (STAR, SUN, NADIR/LIMB, ...)                                       
    Positions on the CCD                                                      
    Parameters list and meaning                                               
                                                                              
                                                                              
Definitions:                                                                  
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Though the file is self documented, the following definitions                 
are useful.                                                                   
                                                                              
Altitude  Computed with MARS ellipsoid (Spice kernel)                         
                                                                              
Longitude positive eastward                                                   
                                                                              
LOS          Line of Sight, this line is related to the center of CCD         
             row 144                                                          
                                                                              
MNP          Mars Nearest Point of the LOS                                    
                                                                              
                                                                              
1stB, 2ndB, 3rdB, 4thB, and 5thB are center of UV Bands (binning included)    
             The IR LOS corresponds to the 3rdB LOS (IR FOV is 1 deg)         
                                                                              
EMEJ2000     Earth Mean Equator, dynamical equinox of J2000.                  
                                                                              
MarsJ2000    MARSIAU frame (Mars Mean Equator and IAU vector of J2000).       
                                                                              
MEX          Mars Express                                                     
                                                                              
Computation background:                                                       
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The computation of geometrical parameters is TARGET dependant.                
                                                                              
For point source (STAR)                                                       
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    The LOS and 1stdB, 2nddB,3rdB,4thdB and 5thdB parameters are computed.    
    The Line of sight is fully defined by the spacecraft position and         
    the direction of the star.                                                
    So, attitude file is not needed to compute most of parameters.            
                                                                              
    For 1stB, 2ndB, 3rdB, 4thB, and 5thB, we need to know the S/C X axis, and 
    now we need the attitude file.                                            
                                                                              
For extended sources (NADIR, LIMB, SUN)                                       
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    The 1stdB, 2nddB,3rdB,4thdB and 5thdB parameters are computed.            
    To compute geometrical parameters, we need to read the                    
    attitude file which gives the directions of the S/C axes.                 
                                                                              
                                                                              
For more details about the geometry computation, please read the              
SPICAM_POINTING_xxx.TXT file.